This invention relates to a method of producing chip-type electronic devices having a semiconductor element such as a diode or a transistor mounted to a substrate.
Small-size chip-type light-emitting devices making use of a light-emitting diode (LED) chip have been in use as a light source. FIG. 5 shows a prior art example of this kind of chip-type light-emitting device 20 with a substrate 2 on which is formed a pair of electrode patterns 3 and 4 made of an electrically conductive material, one of these electrode patterns (3) being composed of portions which may be referred to individually as a top surface electrode 3a, a side surface electrode 3b and a bottom surface electrode 3c and the other of the electrode patterns (4) being also composed of a top surface electrode 4a, a side surface electrode 4b and a bottom surface electrode 4c. Both end edges of the substrate 3 are provided with a sectionally semi-circular groove (or a throughhole) 7 or 8, and the side surface electrodes 3b and 4b of the pair of electrode patterns 3 and 4 include an electrically conductive film such as a solder layer formed on the inner surfaces of these grooves 7 and 8. The bottom surface electrodes 3c and 4c are both electrically connected to a wiring pattern on a printed circuit board (not shown). A pad 3p is provided to the upper surface electrode 3a of one of the electrode patterns (3), carrying thereon an LED diode 1 attached thereto by die bonding. The LED 1 has an electrode 1a which is electrically connected to one end 5a of a metallic wire 5 by wire bonding. The other end 5b of the metallic wire 5 is electrically connected to the top surface electrode 4a of the other of the pair of electrode patterns (4). The LED chip 1 and the metallic wire 5 thus connected to the electrode 1a of the LED chip 1 and the top surface electrode 4a are both completely sealed inside a transparent resin mold 6 which is formed so as to cover only a limited surface area on the substrate 3 retracted from the positions of its end edges such that the material for the mold 6 will not flow through the grooves 7 and 8 to the bottom side.
When the device 20 thus formed is mounted to a printed circuit board, it is transported by using a chuck to lift it by having the part of the mold 6 adsorbed thereby. Since the part of the mold 6 is intentionally made smaller than the entire surface of the substrate 2, as explained above, this means that the area by which the chuck can adsorb the device 20 is very small. In the case of a miniaturized device with the length-width dimension less than 1.6xc3x970.8 mm, for example, there was a problem in that the mounting to a circuit board could not be carried out smoothly.
There has been another problem with this prior art device 20 because the mold 6 makes a surface-to-surface contact with the top surface of the substrate 2, as well as with the top surface electrodes 3a and 4a of the pair of electrode patterns 3 and 4. Because of this structure, an external force such as a vibrational force or an impulsive force which may be experienced tends to cause the bottom surface of the mold 6 to become separated from the surface of the substrate 2 and the electrode patterns 3 and 4, thereby adversely affecting the sealed condition of the LED chip 1 and the metallic wire 5.
It is therefore an object of this invention to provide a method of producing improved chip-type electronic devices which can be mounted more efficiently and with which the shifting of the mold due to an external force can be prevented.
A chip-type electronic device embodying this invention, with which the above and other objects can be accomplished, may be characterized as comprising a substrate having a vertically extending groove formed on each of its mutually opposite edges, a solder material filling these grooves partially to a height which is below the top surface of the substrate, electrode patterns formed on these edges of the substrate, a semiconductor element on the top surface of the substrate, and a resin mold sealing the semiconductor element therein, extending to positions of the edges of the substrate and protruding partially into these grooves. With a device thus characterized, the resin mold, although horizontally extended to the positions of the edges of the substrate, is prevented by the solder material partially filling the grooves from flowing through the grooves to the bottom surface of the substrate, and the side surface electrodes are not covered entirely by the resin mold. Since the resin mold extends to the positions of the both edges of the substrate, its surface area is increased from that of the prior art device shown in FIG. 5, which makes the mounting of the device easier by means of a chuck. Since portions of the resin mold which protrude into the grooves and serve as hooks to more securely fasten the mold to the substrate, the mold, even if subjected to an external force, is not likely to become separated from the substrate.